The present invention relates to a comparator for comparing a first input voltage and a second input voltage to produce an output voltage and relates also to a comparator for comparing a first input current and a second input current to produce an output voltage.
A conventional comparator is disclosed in the Technical Study Report in the Transactions of the Institute of Electronics, Information and Communication Engineers, ICD 89-115, Vol. 89, No. 205, September 1989, pages 25 to 31. This conventional comparator comprises an amplifier unit and a latch unit connected to the amplifier unit. The amplifier unit comprises first through fourth amplifiers, four capacitors connected to the amplifiers, and a plurality of switches connected to the amplifiers. The first amplifier has a voltage input terminal and a reference voltage input terminal. The voltage input terminal is supplied with an input voltage. The reference voltage terminal is supplied with a reference input voltage.
This conventional comparator produces a difference voltage of the input voltage and the reference input voltage to amplify the difference voltage. On the other hand, the conventional comparator is incapable of preventing a large noise voltage which is caused by incidental capacitive coupling. Consequently, inasmuch as the large noise voltage is included in the difference voltage, the conventional comparator is incapable of reliably operating.
Another conventional comparator is disclosed in Japanese Patent Prepublication No. 102807/1993 (Tokkai Hei 5-102807). This conventional comparator comprises a first power terminal, a second power terminal, a first resistor and a first current source directly connected between the first and the second power terminals, a second resistor and a second current source directly connected between the first and the second power terminals, and a comparing unit connected to a node between the first resistor and the first current source and to a node between the second resistor and the second current source. The first resistor is supplied with an input current. The second resistor is supplied with a reference input current. The comparing unit is supplied with an input voltage corresponding to the input current and with a reference input voltage corresponding to the reference input current.
This conventional comparator converts the input current and the reference input current into the input voltage and the reference input voltage to compare the input voltage and the reference input voltage. Namely, this conventional comparator does not compare the input current and the reference input current. In addition, the comparing unit is incapable of speedily operating. Consequently, the conventional comparator is incapable of speedily operating.